Generally relatively high water pressure for the purposes described has been obtained heretofore by mechanically driven piston pumps. The piston pumps which have been used previously usually can only supply pressures below 2500 bar and are not only quite sizable, but also relatively expensive so that their versatility is greatly limited. It is also difficult to maintain a constant speed of such pumps, so that the flow will be constant, without special equipment.
Hydraulic pressure accumulators with which much higher water pressures can be obtained, e.g. pressures of the order of 4000 bar, have been provided heretofore with pistons which are hydraulically reciprocated in respective cylinders and which carry plungers displaceable in their cylinders and serving to alternately displace the water through valve systems to the discharge passage.
The pressure used to drive the piston is oil, for example, under pressure from a motor-driven pump. These pressure amplifiers have a ratio of the effective cross section of the piston to that of the plungers of the order of 10:1 to 20:1 and thus are capable of similarly modifying the pressure between the primary fluid and the secondary fluid.
In pressure amplifiers of this type, mechanical or electric sensors monitor the approach of the piston to the end of its path in each direction of travel and provide an appropriate signal or pulse to operate the valves or distributors reversing the fluid feed to the chambers of the cylinder in which the piston is reciprocated.